1 Field Of The Invention
The present invention relates to sensitive elements for the photomechanical production of multi-color images without printing. The invention has particular relevance to production of color proofs in which at least one color is metallic in appearance. The invention is applicable to both overlay and surprint proofs in either the positive or negative acting modes.
2. Background of the Art
In printing pictorial matter, whether by lithography, letterpress or gravure, the half tone process is generally used, wherein the actual printing image is composed of thousands of minute dots per square inch of a single color ink of varied dot size or ink density. What the naked eye sees as shading in half tone prints is actually the controlled variation in the size of the dots relative to the unprinted areas between the dots. In black and white pictorial matter the dots are printed in black ink only. Full color reproductions, however, are necessarily printed in each of at least three colors, cyan, magenta, and yellow (known as "three color process"), on in these same colors with the addition of black ("four color process"). For each color a separate printing plate is made. In order to make the three or four printing plates, the original color picture or photograph is "separated" either photographically with a camera using filters, masks, etc. or electronically with a color scanner, each separation or individual color information source representing one of the colors, and containing, dot for dot, the amount of that color which must be printed to produce the desired total color print. The preparation of the color-separations and individual color information source is an art and requires considerable skill in handling many variables to produce a desired result. Often trial and error is involved, requiring correction or replacement of one or more of the separations or color sources. Unless some reliable system is available to "proof" the separations or color sources, the printing press must be set up and copy printed just to secure preliminary proofs. This is time consuming and expensive. It is therefore desirable to provide accurate means for proofing the separations or electronically stored color sources without printing.
There are four types of color proofs, a) overlay negative acting, b) overlay positive acting, c) surprint negative acting, and d) surprint positive acting. U.S. Pat. No. 3,136,637 discloses type a) proofing. A light-sensitive transparent sheet is provided for each of the colors to be printed. Each of the sheets is exposed through its respective color separation negative. Upon processing, the color in the non-image areas is removed, yielding a sheet which contains the desired color pattern in the image areas, while being colorless and transparent in the non-image areas (e.g. between halftone dots). After they are assembled together in registry on a white background, a color proof results.
U.S. Pat. No's. 4,250,242 and 3,211,553 describe a positive acting overlay proofing material (type b) above) in which separation positive films are used. In this case the imaged (exposed) areas are removed on processing to yield similar halftone color images which may be assembled together in registry on a white background to give a color proof.
U.S. Pat. No. 3,671,236 describes a negative acting surprint proofing material (type c) above) in which photo-mechanically produced images corresponding with each color are integrally built up on a single substrate (much as occurs in the actual printing operation itself) without any printing operations. The multiplicity of carrier films is eliminated by transferring individual color images from a sheet comprised of (1) a carrier with release surface, (2) pigment and binder layer, (3) photohardenable or insolubilizable layer, (4) barrier layer and (5) pressure-sensitive adhesive layer.
Similarly U.S. Pat. No. 4,260,673 describes a positive acting surprint proofing material (type d) above) in which a positive acting diazo oxide photosensitive layer is used. The color proofing sheet is comprised of a color layer, a binder layer, both being light sensitive, and non-light sensitive solvent resistant barrier layer with the binder layer being present to provide a means of eliminating residual toning between adjacent layers in the structure. This layer may also act as a thermal, adhesive layer to transfer individual color images to a single support forming a surprint proof.